Heretofore, it has been well known to meter flowable solids products by use of mechanical metering devices such as rotary valves, augers, airlocks, and the like. Inasmuch as many solids products are highly abrasive and create high-wear conditions for metering components having moving parts, high maintenance is required to maintain the integrity and operation of such systems. Further, maintenance of a system produces unwanted downtime. Moreover, the mechanical metering devices can cause mechanical shear of the product that is undesirable.
An example of a mechanical metering device employing a rotary valve is disclosed in U.S. Pat. Nos. 6,273,153 and 6,425,529, while an example of a mechanical airlock-type metering device is disclosed in U.S. Pat. No. 5,803,673. It has also been known to pneumatically convey flowable solids materials by use of an air supply and eductors, as shown in U.S. Pat. No. 6,368,028.